Nanoparticle, Size, Shape, and Interfacial Effects on Leakage Current Density, Permittivity, and Breakdown Strength of Metal Oxide−Polyolefin Nanocomposites: Experiment and Theory

A series of 0−3 metal oxide−polyolefin nanocomposites are synthesized via in situ olefin polymerization, using the following single-site metallocene catalysts: C 2 -symmetric dichloro[ rac -ethylenebisindenyl]zirconium(IV), Me 2 Si( t BuN)(η 5 -C 5 Me 4 )TiCl 2, and (η 5 -C 5 Me 5 )TiCl 3 immobilized on methylaluminoxane (MAO)-treated BaTiO 3, ZrO 2, 3-mol %-yttria-stabilized zirconia, 8-mol %-yttria-stabilized zirconia, sphere-shaped TiO 2 nanoparticles, and rod-shaped TiO 2 nanoparticles. The resulting composite materials are structurally characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), 13 C nuclear magnetic resonance (NMR) spectroscopy, and differential scanning calorimetry (DSC). TEM analysis shows that the nanoparticles are well-dispersed in the polymer matrix, with each individual nanoparticle surrounded by polymer. Electrical measurements reveal that most of these nanocomposites have leakage current densities of ∼10 −6 −10 −8 A/cm 2; relative permittivities increase as the nanoparticle volume fraction increases, with measured values as high as 6.1. At the same volume fraction, rod-shaped TiO 2 nanoparticle−isotactic polypropylene nanocomposites exhibit significantly greater permittivities than the corresponding sphere-shaped TiO 2 nanoparticle−isotactic polypropylene nanocomposites. Effective medium theories fail to give a quantitative description of the capacitance behavior, but do aid substantially in interpreting the trends qualitatively. The energy storage densities of these nanocomposites are estimated to be as high as 9.4 J/cm 3 .